(i) Field of the Invention
The present invention relates to an image defect detection apparatus and method, particularly relates to an image defect detection apparatus and method for detecting a defect in the images of photomasks (reticles) and the like.
(ii) Description of the Related Art
Conventionally, there are two image defect detection methods using image processing to inspect a photomask (reticle), etc. used in the semiconductor device manufacturing process. The one is the die-to-die for comparison of same patterns in different positions in real patterns and the other is the die-to-database for comparison of a real pattern with a designed pattern (usually, CAD data). These methods are shown for example in Japanese Patent Application Laid-Open No. 10463/1996 or Japanese Patent Application Laid-Open No. 76359/1996. However, in consideration of future miniaturization of photomasks patterns, there are problems in inspecting them by said two inspection methods. When a pattern is different in size from another pattern of the different position on the same photomask, even though the level of the difference is negligible in the inspection, the pattern is judged as a defect in the die-to-die.
Usually in the die-to-die, the sensitivity of inspection should be suppressed to prevent a false defect(a seeming defect occurred by inaccurate inspection of a product to be passed in a test) caused by the dispersion of products to be passed in a test, because respective patterns existing in distant positions on the same photomask are compared each other.
On the other hand, in the die-to-database, a pattern image should be generated from a designed data to compare the designed data with a real pattern image. The false defect occurs, if the pattern image generated from the designed data is not very coincident with the real pattern image.
In the real pattern image, there is the dispersion of products to be passed in a test on the same photomask as shown above. This means that somewhat different spots occur by said reason, if an image is generated from a designed data based on a pattern.
In addition, regardless of the die-to-die and the die-to-database, the reproducibility of an image is not satisfactory because of an effect of vibration, etc. of a stage carrying a photomask an optical device for sensing in processes before the collection of the image.
In the recent years, the size of a defectxe2x80x94necessary in detectionxe2x80x94has gradually become smaller according to miniaturization of a pattern. Particularly, image defect based on a size or an image defect based on a position increasingly become difficult to detect.
Another image defect detection apparatus and method has been described in Japanese Patent Application Laid-Open No. 200372/1983. However, the art described in that is only a method of compressing a digital image information to simplify the conversion treatment circuit in the image processing, and a method to detect an image defect has not been disclosed.
In addition, in Japanese Patent Application Laid-Open Nos. 215118/1990 and 249656/1995, an mask inspection apparatus and method has been disclosed. However, a use of transmitted rays has been only described; a method for enlargement and reduction of an image has not been described.
Further, in Japanese Patent Application Laid-Open No. 76359/1996, the combined use of transmitted rays and reflected rays in the inspection of a mask has been described, and in Japanese Patent Application Laid-Open No. 304997/1996, a method for comparison of each image datum, that was made by enlarging and reducing one image datum of two image data, with the other image datum in image inspection. However, cancellation of an error caused by an effect of an optical error, vibration, etc. is impossible by this method.
It is an object of the present invention to provide a speedy and precise image defect detecting apparatus and method which can judge negligible difference in size of a products, such as photomask (reticle) and the like, by improving a defect of said conventional arts.
The present invention adopts the constitution of arts described below in order to achieve the above object.
The first aspect of the present invention is an image defect detection apparatus comprising a means to make two copied inspection images from a single inspection image, the first image processing means to carry out image processing applying an expansion filter and a contraction filter in the order to the one copied inspection image, the second image processing means to carry out image processing applying a contraction filter and an expansion filter in the order to the other copied inspection image, and a means to output image information made from differential values of image information outputted from said respective first image processing means and second image processing means.
The second aspect of the present invention is a image defect detection apparatus comprising a data conversion means to convert the inspection image to digital image information, the first memory means to store said digital image information outputted from said data conversion means, the second memory means and the third memory means copying digital image informationxe2x80x94stored by said first memory meansxe2x80x94to store individually, the first processing means to execute the first process by using an expansion filter for digital image information stored by said second memory means, the second processing means to execute the second process by using a contraction filter for digital image information yielded from the result of computing by the first processing means, the third processing means to execute the second process by using a contraction filter for digital image information stored by said third memory means, the fourth processing means to execute the first process by using the expansion filter for digital image information yielded from the result of computing by the third processing means, the fifth processing means to compute the differential values of respective sets of digital image information yielded from the results of computing by the second processing means and the fourth processing means, and the fourth memory means to store the result of computation by the fifth processing means.
The third aspect of the present invention is a image defect detection method determining presence or absence of an image defect in a given inspection image, wherein at least two image copies are made from the digital image information of the inspection image obtained by digital processing of the inspection image, the first processing information is yielded by processing the first processing means using the expansion filter and the second processing means using the contraction filter in such order for the one copied digital image information, and also the second processing information is yielded by processing the second processing means using the contraction filter and the first processing means using the expansion filter in such order for the one copied digital image information, and from the result the differential values of the first processing information and the second processing information are computed, and presence or absence of an image defect in the inspection image.